INTRODUCTION TO PLANT BREEDING

AGRONOMY 815 / COURSE NOTES

P. STEPHEN BAENZIGER, 338 Keim Hall, 472-1538

DEPARTMENT OF AGRONOMY / UNIVERSITY OF NEBRASKA

VARIATION FROM SEXUAL HYBRIDIZATION
HOW ARE PARENTS CHOSEN?

Fehr, Chapt. 10.

Why is variation important? Johannsen experiments in bean weight selection.

When he selected within a pure line, no progeny improvement was obtained. Basically, all of the genetic variation was fixed within the line. Any selection was based on environmentally induced weight differences. Without genetic variation (heritable variation -- progeny), selection is fruitless.

GENETIC DIVERSITY IS MOST COMMONLY OBTAINED BY SEXUAL HYBRIDIZATION ALLOWING NEW GENE COMBINATIONS.

When considering parents:

1. Define the trait you need genetically. Is it single or multigenic? Is it heritable?



2. Define the trait you need objectively. Is it for genetic diversity, for improved yield, for stress tolerance, etc.? Are you selecting both parents or just one parent?



3. Review the possible genetic resources for the trait (trade-off between variation and diversity with the need for a high mean for productivity). NOTE: a high mean requires using adapted types, but variation may require using germplasm outside your normal gene pool.



1. Do you want to use wild species or genera? If so, does your other parent have crossability genes. Will the trait be stable in the cross (e.g., leaf rust suppressor genes in the D genome of wheat)?



2. Unadapted types? How do you regain adaptation and quality? Even if the gene(s) you are interested in transferring are monogenic, you may have introduced multigenic secondary effects including linked traits for quality and adaptation.



3. Adapted types? Will there be enough genetic variation for useful selection?



4. d. Is the parent a population and/or an inbred line?



4. Define the type of end product that you want:



1. inbred line;



2. hybrid;



3. synthetic or population.



5. Choose your breeding method.

One of the most critical aspects in plant breeding is the successful selection of parental material. Mention Rasmusson's comments on crossing bad x bad lines and his using an old barley.

The concept of genetic vulnerability. Note: it is independent of the amount of germplasm that is preserved. Comment on Siouxland and how widely it was grown. Also the rapid loss of the Lr24 and Lr26 resistance complex for leaf rust resistance.

Note: Virtually all of the first third of the course was related to the genetics of hybridization.